Abstract
During its investigations into a series of ten aircraft crashes from 1979 to 1981, US National Transportation Safety Board (NTSB) officials were presented with a hypothesis that “several” of the crashes could have been caused by pilot impairment from breathing oil fumes inflight. The NTSB and their industry partners ultimately dismissed the hypothesis. The authors reviewed the crash reports, the mechanics of the relevant engine oil seals, and some engine bleed air data to consider whether the dismissal was justified. Four of the nine aircraft crash reports include details which are consistent with pilot impairment caused by breathing oil fumes. None of the tests of ground-based bleed air measurements of a subset of oil-based contaminants generated in the engine type on the crashed aircraft reproduced the inflight conditions that the accident investigators had flagged as potentially unsafe. The NTSB’s conclusion that the hypothesis of pilot incapacitation was “completely without validity” was inconsistent with the evidence. Parties with a commercial conflict of interest should not have played a role in the investigation of their products. There is enough evidence that pilots can be impaired by inhaling oil fumes to motivate more stringent design, operation, and reporting regulations to protect safety of flight.
Highlights
With the exception of the Boeing 787, commercial and military aircraft are designed to “bleed” ventilation air, either off the main aircraft engine compressors or from an auxiliary compressor when the aircraft is on the ground
Between 1979 and 1981, National Transportation Safety Board (NTSB) investigators suggested that inhaling oil fumes inflight may have been a causal factor in “several” fatal crashes of turboprop aircraft
“extreme chemical sensitivity” [16] (p. 28) to chemicals in oil fumes, the NTSB and their industry partners soundly dismissed the hypothesis that oil fumes may have impaired some of the pilots on the crashed planes, affirming that it was “completely without validity” [16]
Summary
With the exception of the Boeing 787, commercial and military aircraft are designed to “bleed” (or extract) ventilation air, either off the main aircraft engine compressors or from an auxiliary compressor when the aircraft is on the ground This hot compressed “bleed air” is cooled, dehumidified, typically mixed with some fraction of recirculated air, and routed to the cabin and flight deck for ventilation and pressurization [1]. To greater or lesser degrees—engine oil can contaminate the compressed air, whether it migrates across engine seals, spills from an overserviced reservoir, or is vented improperly, for example [2] The problem with this design is that a fraction of that compressed air is bled off the engine and routed to the air conditioning system for cabin ventilation and pressurization. One of the early references to pilots breathing “hot oil fumes” inflight acknowledged that “the symptoms in these cases have been similar to those of carbon monoxide poisoning,” but noted that various aldehyde breakdown products are “probably the causative agents,”
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